Surprisingly, there is no documentation on the official site http://virt-manager.org/ I specifically need documentation on bridged / host-only / NAT virtual networking via the GUI.
It depends on your version of virt manager
In your guest, select host networking
If your version of virt manager does not automatically add a bridge you need to manually configure your bridge.
You might found all required instruction on this site https://www.linux.com/learn/create-and-run-virtual-machines-virt-manager
There is a section at the beguining about bridged networking